1. Field of the Invention
The present invention is directed to a tool for use in drilling earthen wells. The present invention is directed to a stabbing guide adapted for use with a consumable saver sub coupled to the output drive shaft of a top drive.
2. Description of Related Art
A top drive is a hydraulic or electric motor suspended from the derrick of a drilling rig that rotates the drill string and drill bit for drilling a well. Using a top drive eliminates the need for the conventional kelly and rotary table, and it reduces the amount of manual labor and associated hazards that have traditionally accompanied this task. For drilling contractors and casing installers, utilizing top drive technology translates into improved operational efficiency.
Top drives can be used to rotate a tubular segment to threadably make up a connection between the tubular segment and a tubular string that is lowered into a borehole as it is lengthened. Top drives couple to tubular segments with threads, as is shown in FIG. 1. The male threads 4 of the top drive output shaft 3 are threadably received into mating female threads 8 in the upwardly disposed end of the tubular segment 6.
A problem resulting from repeated make up and break out of threaded connections using a top drive is that the threaded male member 4 coupled to the output drive shaft 3 of the top drive 2 becomes worn and damaged with repeated use. Replacement of the threaded male portion 4 of the top drive 2 is expensive and time consuming if the top drive is taken out of service.
A saver sub is a short length of drill collar that serves as an extension for the output drive shaft of the top drive. The saver sub has a threaded male coupling at one end, a threaded female coupling at the other end and a bore there through, and the threaded female end of the saver sub receives and threadably fastens onto the downwardly disposed threaded male member that is coupled to the output drive shaft of the top drive. The opposed threaded male end of the saver sub is received into and threadably fastened to the tubular string that extends into the borehole.
When the hole must be deepened, and when a tubular segment must be joined to lengthen the tubular string, the threaded connection between the saver sub and the rest of the tubular string is disconnected, as opposed to disconnecting the connection between the top drive and the saver sub, so that the connection between the top drive and the saver sub is rarely disconnected and reconnected and, therefore, it endures minimal wear and tear. Although the lower threaded connection between the saver sub and the tubular string is used repeatedly and endures almost all of the wear and tear, the saver sub is designed to be consumable. That is, the saver sub is adapted for periodically being removed from the top drive output drive shaft, re-machined to restore the lower threaded male end to good working order, and the saver sub can be returned to service. Although removal of the damaged threads and re-machining new threads onto the saver sub consumes some of the length of the saver sub, the saver sub may be restored a number of times until it becomes too short to be used. The saver sub is expendable and does not represent a major investment. However, the top drive output drive shaft threads are spared considerable wear and tear by use and restoration of the sacrificial saver sub, and the top drive components represent a significant capital cost and considerable rig downtime when replaced.
A problem that arises from the use of saver subs is the difficulty in obtaining proper alignment of the top drive with the tubular segment to which it is being coupled. As shown in FIG. 2, the tubular segment 7, which can range from 30 to 93 feet in length, may be moved off center alignment with the top drive 2 by wind or by very slight imperfections or wear in the tools used to grip and hold the tubular segment 7 for make up of the connection with the top drive 2. The top drive 2 is extremely heavy and advances downwardly with great force. Consequently, misalignment of the top drive 2 and the tubular segment 7 when attempting to make up the connection between the two can result in substantial damage. Plastic deformation resulting from misaligned impact may cause leaks in the pipe string due to damage to the sealing surfaces 9 of the threaded connection.
What is needed is a tool for preventing misalignment upon introduction of the top drive saver sub into the connection on the tubular segment. What is needed is a tool for reliably aligning the tubular segment with the top drive saver sub so that the threaded connection can be made up without damage to the connection.